PARAMETER

, a certain constant right line in each of the three Conic Sections; otherwise called also Latus Rectum.

This line is called Parameter, or equal measurer, because it measures the conjugate axis by the same ratio which is between the two axes themselves; being indeed a third proportional to them; viz, a third proportional to the transverse and conjugate axes, in the ellipse and hyperbola; and, which is the same thing, a third proportional to any absciss and its ordinate in the parabola. So if t and c be the two axes in the ellipse and hyperbola, and x and y an absciss and its ordinate in the parabola; then the Param. in the former, and the Param. in the last.

The Parameter is equal to the double ordinate drawn through the focus of any of the three conic sections.